The blazar-like radio structure of the TeV source IC310

TL;DR

This study reveals that the TeV source IC310 exhibits blazar-like radio jet structures on parsec scales, suggesting a low-luminosity FRI galaxy with a jet orientation close to our line of sight, which may explain its high-energy emission.

Contribution

First high-resolution VLBA imaging of IC310's parsec-scale radio structure, showing blazar-like features and jet orientation consistent with gamma-ray observations.

Findings

Detected a one-sided core-jet structure aligned with larger-scale radio features.

Jet orientation angle estimated to be less than 38 degrees, indicating beamed emission.

Jet stability from parsec to kiloparsec scales argues against headtail morphology.

Abstract

Context. The radio galaxy IC310 in the Perseus cluster has recently been detected in the gamma-ray regime at GeV and TeV energies. The TeV emission shows time variability and an extraordinarily hard spectrum, even harder than the spectrum of the similar nearby gamma-ray emitting radio galaxy M87. Aims. High-resolution studies of the radio morphology help to constrain the geometry of the jet on sub-pc scales and to find out where the high-energy emission might come from. Methods. We analyzed May 2011 VLBA data of IC310 at a wavelength of 3.6 cm, revealing the parsec-scale radio structure of this source. We compared our findings with more information available from contemporary single-dish flux density measurements with the 100-m Effelsberg radio telescope. Results. We have detected a one-sided core-jet structure with blazar-like, beamed radio emission oriented along the same position angle as the kiloparsec scale radio structure observed in the past by connected interferometers. Doppler-boosting favoritism is consistent with an angle of theta < 38 degrees between the jet axis and the line-of-sight, i.e., very likely within the boundary dividing low-luminosity radio galaxies and BL Lac objects in unified schemes. Conclusions. The stability of the jet orientation from parsec to kiloparsec scales in IC310 argues against its classification as a headtail radio galaxy; i.e., there is no indication of an interaction with the intracluster medium that would determine the direction of the tail. IC310 seems to represent a low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type central engine.